Alert dialog

The sharpest line to draw is role="alertdialog" against role="dialog". Both open a window that takes the page over, and to a sighted reader they look identical. The difference is what a screen reader does on arrival: a plain dialog is announced as a dialog and then read at the reader’s own pace, while an alert dialog is announced at once, message and all, the way a live alert would be. The role is therefore a claim about consequence, not about content. It says this window appeared because something is about to happen, so hear it now rather than when you get to it.

That makes the role narrow. Anything the reader asked for is a plain dialog, however important it looks: a settings sheet, a compose window, a form. An alert dialog is for the window that arrives because a destructive action is in flight, a session is about to expire, or work is about to be lost. Ship one for a routine confirmation and the assertive announcement is worth nothing, because a reader who is interrupted every time stops treating the interruption as information.

Three words in this vocabulary sit at three different levels, which is why they are so easy to blur. Modal dialog is the container: a window over a scrim with focus moved in, focus trapped, Escape wired, and the page behind it inert. Confirmation dialog is the pattern: stopping an action part way through to ask whether it was meant, with the consequence named in the confirm button. Alert dialog is the role the second usually wears inside the first. A confirmation dialog is almost always built as an alert dialog, and saying it that way keeps all three words useful: the container, the pattern, and the announcement.

The near miss on the other side is the message that does not block. A toast reports something that already happened and cleans itself up, and a live region announces without taking focus at all, so both are for news rather than for decisions. Reach for an alert dialog only when there is a question the product genuinely cannot proceed without. When you do, give it a title naming the consequence, a description wired with aria-describedby so the announcement carries the detail, and initial focus on the safe answer rather than the destructive one, because assertive announcements and a pre-aimed Delete button are a bad pairing for anyone pressing Enter out of habit.